1. Field of Invention
This application relates to both radio frequency as well as free space optical data communication, particularly to transceiver alignment.
2. Description of the Related Arts
In 2003, the FCC-licensed for use 13 GHz of spectrum in the 70 GHz and 80 GHz bands, also known as the E-band millimeter wave Radio Frequency (RF) spectrum. Ten bands in this spectrum were made commercially available for a broad range of fixed wireless applications operating at gigabit data transfer rates. Applications include point-to-point local wireless networks and broadband internet access. Communication of data through E-band signals potentially serves as a cheap alternative to more costly fiber solutions, particularly in urban areas due to the cost of laying fiber. E-band RF data transfer is a particularly cost effective solution for filling the gap for short-haul wireless connectivity in the so-called “last mile” between network service providers and customers. E-band RF data transfer can also offer data rates that overlap with lower the end of rates available with fiber-based solutions.
Because of its location in the radio frequency spectrum (71-76 and 81-86 GHz), E-band data transmission is not very susceptible to interference due to fog, airborne particulates such as dust and atmospheric turbulence. E-band data transmission, however, is susceptible to degraded performance due to rain. Rain interferes with radio wave transmission in the E-band such that during a rain storm, data transmission would necessitate repeated data retransmission at best or interrupted service at worst. Further, radio waves in the E-band have a narrow, pencil beam-like characteristic, and as a result antennas producing E-band signals can be placed in close proximity to one another without concern for adjacent channel interference. However, due to the narrow pencil-like characteristic of the E-band RF beam, an E-band transmitter must be precisely pointed at its receiver in order to ensure data transmission.
Free-space optical communications links can also be used advantageously in telecommunications. Compared to other communications technologies, a free-space optical communications link can have advantages of higher mobility and compact size, better directionality (e.g., harder to intercept), faster set up and tear down, and/or suitability for situations where one or both transceivers are moving. Thus, free-space optical communications links can be used in many different scenarios, including in airborne, sea-based, space and/or terrestrial situations. An FSO transceiver that outputs an optical signal with wavelengths centered about 1550 nanometers is eye-safe and can be adapted to FSO commercial communications. FSO transmission is, however, subject to disruptions due to fog, snow, airborne particulate matter, and atmospheric turbulence. Additionally, FSO signals are transmitted as optical beams, and thus are even narrower and require even more precise alignment than RF beams.
Further, twist and sway movements due to wind and other weather can easily disrupt both E-band and FSO data transmission versus data transmissions that occurs at lower frequencies.